The following U.S. Patent Publications are believed to represent the current state of the art and are hereby incorporated by reference:    U.S. Published Patent Application No. 2008/0278353;    U.S. Pat. Nos. 7,270,275; 6,646,565; 6,917,299 and 4,486,637;    European Patent Nos.: 1421549 and 1676182; and    Great Britain Patent Application No. GB8608277.